If you want to main tank, on either class, you need to get to the point that you are not a limiting factor on your dds. A great place to test this is Apep. Get your best DD, a who, and you. See if you can pull him and hold him while your dd goes as hard as possible (while still using enmity down cool downs). Once you have the gear approach to get to the point you don't slow that dd down, you're ready.

As people have said, many use War on early rooms switching to PLD at first boss. I do this for our 17min runs, but its not necessary for 25m runs.